The present invention relates to a lubricant varnish coating component, a lubricant varnish prepared therewith and methods for coating elastomers, for example, elastomer profiles, such as windshield wiper blades, using this lubricant varnish.
Windshield wiper blades are generally able to adapt to the contour of the windshield of the motor vehicle and remain flexible even at different temperatures. Wiper blades are, generally, therefore produced from elastomer profiles and rubber materials, such as natural rubber or chloroprene rubber. In addition, wiper blades may be made of silicone rubber or polyurethane rubber.
Compared to materials such as glass or plastic, elastomers have high coefficients of sliding friction so that, in the case of a specified vertical contact force of an elastomer profile in the form of a windshield wiper blade on the surface of a glass windshield, a multiple of the contact force may have to be applied for a horizontal movement. If the windshield wiper is operated under wet conditions, a thin lubricating film between the windshield wiper blade and the windshield is formed by the water film on the windshield so that hydrodynamic lubrication is established. However, problems may occur when the windshield wiper blade is operated without water as a lubricating film, for example, during summer or after short rain showers. Under such conditions, the windshield dries quickly, with the result that the coefficient of friction increases sharply, which may lead to squeaking, chattering or even stoppage of the windshield wiper.
Chlorination or bromination of the surface of the windshield wiper blade, i.e. curing, may be carried out in order to reduce the coefficient of friction of windshield wiper blades on a dry glass windshield. However, this may require exact process control and may be problematic in terms of environmental protection.
Conventionally, elastomer profiles may be provided with a coating which, for example, reduces the coefficient of friction under dry conditions, i.e. the coefficient of dry friction, xcexcdry. In Japanese Patent No. 55 015 873, a wiper lip is coated with a silicone rubber into which molybdenum disulfide has been introduced as a dry lubricant for reducing the coefficient of friction. A similar approach is adopted by German Patent No. 38 38 904, in which a polyurethane lacquer is used as a binder, into which graphite powder has been incorporated.
In addition, German Patent No. 38 39 937 describes a one-component polyurethane lacquer which contains reactive polysiloxanes for coating elastomers. European Patent No. 293 084 describes a coating which also contains an additive, such as carbon black, Teflon, graphite or talc, in addition to a polyurethane and a siloxane. Coatings which have a low coefficient of friction under dry conditions may be produced with this material on elastomers.
The lubricant varnish and component according to the present invention, and the method for coating elastomers in accordance with the present invention, provide a coating which has a particularly low coefficient of dry friction, for example, on windshield wiper blades, so that such wiper blades may be used on dry or drying vehicle windshields.
For example, the force necessary for moving the wiper arm over the windshield may be substantially reduced by the coating according to the present invention, so that the electric motor driving the wiper arm may be designed to be smaller. This also may permit the use of more economical motors and reduce the energy consumption in the motor vehicle. Vehicle types in which large, flat windshields are present may require very long wiper arms and wiper blades, for reducing the air resistance.
A reduction of unpleasant noises, such as squeaking or chattering, may be achieved by the coating on windshield wiper blades according to the present invention.
The lubricant varnish and methods according to the present invention provide for a coating on a windshield wiper blade that may ensure constant good wiping quality over a relatively long period, for example, corresponding to the time between the normal inspection intervals of a motor vehicle. The lubricant varnish according to the present invention has very good adhesion to and abrasion resistance on elastomer profiles.
Compared to the conventional halogenation of elastomer profiles, the methods according to the present invention provide that the applied lubricant varnish may be applied reliably with constant quality and simple process engineering. Moreover, the lubricant varnish according to the present invention may be more environmentally friendly.
If the lubricant varnish according to the present invention is present in the form of an aqueous 1-component or 2-component varnish, it may constitute no danger to the environment, the process costs are reduced, and storage is simplified.
The lubricant varnish according to the present invention may be applied in a variety of ways, for example by spraying, dipping or brushing.
In addition, the application of the coating to the elastomers may be effected before their vulcanization, so that the energy supplied during the vulcanization may simultaneously be used for final curing and/or thermal crosslinking, and the final curing of the lubricant varnish may take place in a very short time. Moreover, owing to the higher reactivity of the unvulcanized material, better crosslinking of the coating with the elastomer forming the substrate may be achieved.
The coating may also be applied after the vulcanization. This makes it possible to apply the coating outside the production line for the elastomer profiles.
An isocyanate-based curing agent may be added as a curing agent to the lubricant varnish component.